Electrolytic capacitors may have anodes manufactured from a valve metal powder by suitable compaction thereof to form a coherent porous body which is subsequently processed to produce the dielectric of the capacitor, by anodising the valve metal, and to introduce into or cause formation within the anodised, porous body an appropriate electrolyte liquid or solid respectively.
Since a considerable proportion of the valve metal does not play an active part in the capacity forming mechanism, there has been used a valve metal coated powder to form the porous anode, again using suitable compaction techniques. This approach, which reduces the amount of valve metal required, is particularly attractive from a cost-saving point of view when the valve metal employed is relatively expensive, e.g. tantalum, niobium, or tantalum/niobium alloys.
The core material of the valve metal coated powder may be electrically conducting, as described for example in British Specification No. 1,298,928, but there are some disadvantages in employing certain categories of electrically conducting core material, particularly if it is of a metal or alloy which is not a valve metal, in that compaction of the coated powder may cause the core material to be exposed through the valve metal coating.
Alternatively, the core material may be electrically insulating, typically a ceramic. So far as is known, all anode compaction processes for producing capacitor anodes from valve metal coated ceramic powder have involved a two-stage process in which the powder is first pressed and then sintered, the sintering temperature being at least 1600.degree. C. for tantalum coated alumina powder.
It is an object of the present invention to eliminate the sintering stage, whereby production costs are reduced.